Watch: 5 of YouTube’s craziest abs workouts

While metabolism-spiking HIIT exercises strip fat to get your abs on show, you've got to make sure there's a six-pack underneath your keg. Enter the abs routines: gruelling situps, isometric holds and sadistic twists to set your core on fire. Here's some of the best that YouTube has to offer.

With his shaved head and lean muscle, Frank Medrano looks like an ubermensch grown in a lab. Often labelled a superhuman, this vegan Calisthenics king shows off a tough abs circuit with a cool head and perfect form. Medrano designed this workout to be repeated three times, but we'll be impressed if you can make it through round 2.

Bodybuilding champion Ulisses Jr showcases 50 (yes, 50) of his weirdest, most effective and downright diabolical ab exercises. Ranging from weighted hanging leg-raises to bearcrawls and hanging windscreen-wipers, the 2x musclemania champion flaunts the fruits of his labours. Not one for the faint-hearted.

Brendan Myer's six-pack routine is another floor-only, but these stripped-down circuits are killer when done right. See Brendan perform the routine in real-time, starting off with those nasty leg-raise pulsators. Ouch.

When it comes to calisthenics, the gents at Barstarzz are internet royalty. Here PT Freddy Fox looks at progressive ab exercises, taking you through beginner to advanced. One look at his zero-fat washboard stomach will have you flat on your back doing "x's and o's"

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